The present invention relates to a method of deoxidation casting and a deoxidation casting machine, more precisely relates to a method of deoxidation casting, in which a molten metal left in a feeder head is properly treated, and a deoxidation casting machine capable of executing said method.
There are many kinds of ways of casting aluminum or aluminum alloy. For example, gravity casting can be executed in a simple casting die and is capable of improving quality of products. A conventional method of aluminum gravity casting will be explained with reference to FIG. 14. A splittable casting die 100 is made of a metal and constituted by a lower die section 102a and an upper die section 102b. A cavity 104, in which a product will be cast, is formed between the die sections 102a and 102b. 
A molten metal inlet 106, from which a molten metal, e.g., molten aluminum, is poured, the cavity 104 and a feeder head 108, which is provided between the inlet 106 and the cavity 104, are formed in the upper die section 102b. Further, air ventilation holes 110, which discharge air in the cavity 104 when the molten metal is introduced into the cavity 104, are also formed in the upper die section 102b. 
When the molten metal is solidified, about 3% of volume of the molten metal is contract. By the contraction of the molten metal filled in the cavity, a contracted part is formed in the cast product. In the casting die 100 shown in FIG. 14, the molten metal in the feeder head 108 moves toward the contracted part, by its own weight, when the molten metal in the cavity 104 is solidified. Then, the molten metal fed from the feeder head 108 fills the contracted part, so that no contracted part is formed in the cast products. Since the molten metal is supplemented from the feeder head 108 to the cavity 104 by its own weight, volume of the feeder head 108 must be great.
Fluidity of the molten metal is low in the casting die 100, so weight of the molten metal in the feeder head 108 must be heavy. Therefore, the volume of the feeder head 108 must be great so as to compulsorily supplement the molten metal. In the case of aluminum casting, for example, aluminum is apt to oxidize, so an oxide film is formed on the surface of the molten aluminum, so that the fluidity of the molten aluminum must be lower. To improve the fluidity, lubricant is applied to inner faces of the cavity 104.
To improve the fluidity of the molten aluminum and to cast a product having good external appearance without applying the lubricant, the inventors of the present invention invented a method of aluminum casting (see Japanese Patent Gazette No. 2000-280063). The method will be explained with reference to FIG. 15. A deoxidizing compound, e.g., magnesium nitride compound (Mg3 N2), is introduced into the cavity 104 of the casting die 100, then the molten aluminum or aluminum alloy is poured into the casting die 100. The deoxidizing compound deoxidizes the oxide film formed on the surface of the molten aluminum or aluminum alloy, so that surface tension of the molten aluminum or aluminum alloy can be reduced, the fluidity thereof can be improved, and the product having no casting-wrinkles can be produced. Namely, high quality products can be cast.
The method using the deoxidizing compound is capable of improving the fluidity of the molten metal and well filling the molten metal in the cavity. The volume of the feeder head 108 can be reduced because the molten metal is capable of well filling the cavity 104 without using the weight of the molten metal in the feeder head 108. Therefore, the volume of the feeder head 108 may be designed on the basis of the volume reduction of the solidified metal.
In the conventional casting machine, the metal solidified in the feeder head 108 is integrated with the product solidified in the cavity 104. The metal solidified in the feeder head 108 must be cut and removed from the cast product. The removed metal will be reused as a casting material. As described above, the step of removing a disused solidified metal from the product is an essential step in the conventional method. If the volume of the feeder head 108 is great, it takes a long time to remove the disused metal. Further, energy consumption must be increased so as to melt the disused metal, which has the great volume, to reuse.
On the other hand, in the improved method disclosed in the Japanese Patent Gazette No. 2000-280063, the volume of the feeder head 108 can be designed to supplement the contracted part of the product, so the volume of the feeder head 108 can be reduced. By reducing the volume of the feeder head 108, the volume of the disused metal is also reduced, so the disused metal can be easily cut and removed from the cast product.
However, if the volume of the feeder head 108 is too small, the contracted part is formed in the vicinity of a connecting part between the disused metal and the cast product. In some cases, the contracted part is formed in the cast product. Further, if the molten metal left in the small feeder head 108 can be removed or discharged therefrom, working efficiency of the casting can be improved.
An object of the present invention is to provide a method of deoxidation casting, in which a disused metal left in a feeder head can be easily removed from a cast product, or the molten metal left in the feeder head can be removed from the cast product so as to easily finish the cast product and reduce energy consumption of the casting work.
Another object of the present invention is to provide a deoxidation casting machine capable of executing the method of the present invention.
To achieve the objects, the present invention has following structures.
The method of deoxidation casting of the present invention comprises the steps of:
pouring a molten metal into a cavity of a casting die, which includes a feeder head provided between a molten metal inlet and the cavity; and
reacting a deoxidizing compound with the molten metal so as to deoxidize an oxide film formed on a surface of the molten metal, and
the method is characterized in,
that rate of cooling the molten metal in the feeder head is lower than that in the cavity, and
that the molten metal in the feeder head, which is not solidified, is treated when the molten metal in the cavity is solidified so as to make an outline of a cast product correspond to that of a desired product.
The deoxidation casting machine of the present invention, in which a deoxidizing compound reacts with a molten metal so as to deoxidize an oxide film formed on a surface of the molten metal, comprises
a casting die having a molten metal inlet, a cavity into which a molten metal is poured from the molten metal inlet and a feeder head provided between the molten metal inlet and the cavity, wherein rate of cooling the molten metal in the feeder head is lower than that in the cavity, and
the machine is characterized by,
means for pressing the molten metal in the feeder head, which is not solidified, toward the cavity when the molten metal in the cavity is solidified so as to make an outline of a cast product correspond to that of a desired product.
Another deoxidation casting machine of the present invention, in which a deoxidizing compound reacts with a molten metal so as to deoxidize an oxide film formed on a surface of the molten metal, comprises
a casting die having a molten metal inlet, a cavity into which a molten metal is poured from the molten metal inlet and a feeder head provided between the molten metal inlet and the cavity, wherein rate of cooling the molten metal in the feeder head is lower than that in the cavity, and
the machine is characterized in,
that a cavity constituting member of the casting die is separable from a feeder head constituting member thereof, and
that the cavity constituting member, in which the molten metal is solidified, is separated from the feeder head constituting member while the molten metal in the feeder head is not solidified.
Further, the deoxidation casting machine of the present invention, in which a deoxidizing compound reacts with a molten metal so as to deoxidize an oxide film formed on a surface of the molten metal, comprises
a casting die having a molten metal inlet, a cavity into which a molten metal is poured from the molten metal inlet and a feeder head provided between the molten metal inlet and the cavity, wherein rate of cooling the molten metal in the feeder head is lower than that in the cavity, and
the machine is characterized by,
means for discharging the molten metal is provided to the feeder head, wherein the molten metal in the feeder head, which is not solidified, is discharged outside when the molten metal in the cavity is solidified.
In the present invention, the product can be cast without forming a contracted part. Volume of a disused metal solidified in the feeder head can be reduced, so that the disused metal can be easily removed by proper means, e.g., a milling cutter, and working efficiency can be improved.
If the molten metal in the feeder head, which is not solidified, is removed from the cast product solidified in the cavity, no disused metal is integrated with the cast product. In this case, the molten metal in the feeder head is not solidified, so it can be easily removed from the cast product.
Since the volume of the feeder head can be reduced, energy consumption of the casting work can be reduced, and manufacturing cost can be reduced.
Since the deoxidizing compound formed on inner faces of the cavity contact the oxide film of the molten metal, the fluidity of the molten metal can be improved and the cavity can be well filled with the molten metal without applying lubricant. Further, even if the molten metal is pressurized, the cavity is not damaged. Durability can be improved, maintenance can be easily executed, and a span of life of the casting die can be extended.